Most of New Jersey, including Bergen and Passaic counties, received poor grades again for smog, which can aggravate health problems, but had much better rankings in terms of soot, the fine particles created when vehicles and power plants burn fuel, according to a report released Thursday by the American Lung Association.

While most counties received an "F'' for high ozone days, which can cause difficulties for people with asthma and other ailments, Bergen and Passaic counties received "A''' grades for having no days with high soot, known as particle pollution days, according to the report.

Overall, the 2017 "State of the Air" report found continued improvement in air quality, but a continued increase in dangerous spikes in particle pollution that is putting Americans' health at risk.

"When you look at a long period of time, there's abundant evidence that there's a great decline in the pollution going into the air,'' said Kevin Stewart, director of environmental health at the American Lung Association.

But the 9 million state residents are still getting their share, Stewart said. "It is downwind from significant sources not only in the Philadelphia metropolitan area where concentrations are higher, but the Baltimore-Washington D.C. area that wafts up this way and sources as far out as the Ohio Valley that put out nitrogen oxide that helps create ozone as that air moves east,'' Stewart said.

Bergen reported 22 high ozone days – up from 15 in the report released two years ago – which is still an "F.'' The pollution can cause shortness of breath, damage airways and aggravate lung diseases such as asthma, emphysema and chronic bronchitis. Exposure can also increase the risk of premature death from heart or lung disease. Passaic reported nine high ozone days, scoring a D.

The New York-Newark metropolitan area, which includes parts of New Jersey, New York, Pennsylvania and Connecticut – is ranked ninth for high ozone days out of 228 metropolitan areas nationally, according to the report. Other rankings include 28th for 24-hour particle pollution out of 186 metropolitan areas and 22nd for annual particle pollution out of 184 metropolitan areas

Nationwide, nearly four in 10 Americans lived in counties with unhealthful levels of ozone or particle pollution in 2013-2015, placing them at risk for premature death and other serious health effects such as lung cancer, asthma attacks, cardiovascular damage and low birth weight.

In fact, just a few weeks ago, a study published by a team of scientists showed that New Jersey mothers living as far as 20 to 30 miles downwind from a coal-fired power plant on the Delaware River in Pennsylvania had smaller babies. The study said babies born in Morris, Sussex, Hunterdon and Warren counties from 1990 to 2006 were 17 percent more likely to be born with very low birth weight – under 3⅓ pounds – and 6.5 percent more likely to be born with low birth weight – under 5½ pounds.

New Jersey has made significant progress in improving its air quality, said Caryn Shinske, a spokeswoman for the state Department of Environmental Protection.

"Making changes in one’s ordinary daily routine can do much to reduce ozone pollution, from maintaining energy-efficient vehicles to not idling vehicles while in line, to using environmentally friendly products for cleaning or certain home improvement projects, such as painting,'' Shinske said. "Lifestyle choices impact the air we breathe, and positive changes improve public health.''